Carbon microphone



MBICh' 2,3, 1944- tA. UEBERscHuss 2,345,073

CARBON MICROPHONE Filed March 24, 1941 Patented Mar. 28, 1944 CARBON MCROPHONE Albert Ueberschuss, Berlin-Charlottenburg, Germany; vested in the Alien Property Custodian i Application March 24, 1941, Serial No. 384,829

In Germany February 20,1940

s claims.

This invention relates to a sealed microphone case and has for its object to improve the seal, particularly to reduce the inuence of great fluctuations of temperature on the operation oi' the sealed microphone.

In properly sealed microphone cases the air volume in front or behind the operating diaphragm varies inthe case of great iluctuations oi temperature in such a mannerthat the protective diaphragm when in operation for a considerable time expands and comes into contact with the operating diaphragm so that in the case of an intense cooling it experiences together with the latter a deflection. It has already been proposed to reduce this iniluence by the fact that the air volume ismade as small as possible by inserting iilling material between the case wall on the one hand and the operating diaphragm and the carbon chamber on the. otherA hand. However, this measure does not fulfil the desired requirements in the case of great fluctuations of vantageous from an acoustical point" of view.

temperature. It has also been proposed to miniy mize the influence of difierences in pressure on the operating diaphragm oi' the microphone by closing the rear part of themicrophonecase or the carbon chamber by means of aiiieaible diaphragm, for instance, oi' rubber which may easily expand upon the occurrence oi' 'an inner overpressure and thus brings about a compensation of pressure. However, in the above-mentioned lmown arrangements an absolute tightness cannot be attained, since the operating diaphragm and its bearing points are not sealedat the side opposite the electrode.

The above-mentioned drawbacks are avoided according to the invention by enclosing the4 carbon chamber together with the operating diaphragm in a continuous inner protective casing made of a material which is resistant to corrosion, water-tight and preferably not conducting, said protective casing consisting of a protective diaphragmA and of a ileiiible corrugated pressure compensation diaphragm. In this manner the protective diaphragm necessary for a fprope tightness is protected against the iniiuence of the iluctuations oi pressure occurring.l

inside the microphone, since the pressure compensation diaphragm expands under the inuence of an over-pressure easier and quicker than the protective diaphragm. Furthermore, the iill-l ing material `as, well vas the insulation between the carbon chamber and thenlling material .are dispensed with, since a shunt between the operating diaphragm and the casing cannot occur in case the carbon granules should fall out o! the since the air volume whichv becomes acoustically eilective and is tofbe maintained as small as possible may bev reduced to a further extent. As the protective diaphragm and the pressure compensation diaphragm are so designedy as to form a continuous protective casing', an absolute tightness is attained which is not the case' it the protective diaphragm and the pressure compensating diaphragm are arranged in spaced relation from each other, since the Joints between the operating diaphragm and the contact ring, between the protective diaphragm and the operating diaphragm and between the pressure ring and the protective diaphragm must be separately sealed. The manner in which the'` seal is carried out avoids additional packing rings. The protective4 sure compensation diaphragm between the car-` Y bon chamber and themlcrophone wall as'close as possible to the operating diaphragm and `by bending the edge thereof at right angles by the deep drawing process, the edge being glued with an adhesive substance consisting of the protective casing material to the protective diaphragm I0 contacting with the edge oi' the operating diaphragm 1 or lying on the latter. By also arranging the pressure compensation diaphragm as' close as possible to theoperating diaphragm, the air volume whose expansion isA to be compensated is reduced to a The edge bent at right angles facilitates the rfilstening of the' protective diaphragm and the use oi'. an adhesive substance consisting of the material of the protective casing permitsa particuphragm. In order to facilitate the joiningof the pressure compensation diaphragm and the-protective diaphragm,l the latter may also be bent l kat right angles by the deep drawing process. The

electrical connection of the microphone is established in a known manner through a contact nipfurther extent.` 'i

ple and the microphone case insulated from the contact nipple. The connection with the microphone case and the movable electrode may be obtained in a simple manner by the fact that one or more contact foils which are on the one hand soldered to the microphone wall and on the other hand are secured to the contact ring for the operating diaphragm, pass through the protective casing at the joint between the protective diaphragm and the pressune compensating diaphragm. In order to attain a proper expansion of the pressurecompensation diaphragm the corrugated portion of the pressure compensation diaphragm may have a smaller thickness than the other portions thereof.

In the accompanying drawing are shown some forms of the invention in diagrammatic form, in which Fig. 1 shows a sectional view of one half of the sealed microphone case according to the invention.

Fig. 2 is a part sectional view of another form of the invention, and

Fig. 3 shows a part sectional view of the microphone casing of Fig. l at the point where the contact foil passes.

Referring to Fig. l, I denotes a truncated cone-like case. Its bottom is provided with an opening in which is arranged a contact nipple 2. A resilient cup 3 in which is arranged the fixed electrode 4 is secured to the case I with the aidy of the contact nipple 2. The fixed electrode l forms a part of the casing for the carbon chamber I which is closed at the side, for instance,

by means of a felt strip l which bears against the operating diaphragm 1 integral with the movable contact l. 'I'he edge of the diaphragm 1, a bearing ring 9, a pressure ring I I and a cover plate I2 are rmly secured together with a protective diaphragm Il to the case I by means of a flanged ring I3. Between the cup 3 and the case wall I as well as between the bearing ring l and the wall I are clamped the edges of a pressure compensation diaphragm Il consisting preferably of polyvinyl chlori'de which is particularly resistant to corrosion and weatherproof and which retains its shape despite its small stiffness. The pressure compensation diaphragm I4 has a central cup-like portion I5 which surrounds the electrode I and the resilient cup 3, a corrugated portion i6 as well as an edge I1 bent at right angles by the deep drawing process. The portion I5 and the edge I1 mechanically stressed by the rivet-like contact nipple 2 and the flanged ring I3 are preferably given a relatively large thickness, whereas the portion Il serving to compensate the pressure has a smaller wall thickness. To maintain the air space behind the operating diaphragm small, the pressure compensation diaphragm I4 is arranged as close as possible to the operating diaphragm 1. The edge I1 of the pressure compensation diaphragm Il, bent at right angles engages all joints of the parts lying one upon the other and is glued to the edge of the auxiliary diaphragm I0 as indicated at Il. To this end, an adhesive substance is preferably employed, consisting of the material of which the pressure compensation diaphragm and the protective diaphragm IU are made. The parts III and I4 forming the inner protective casing are preferably made of the same material. The protective diaphragm I0 may lie directly on the operating diaphragm 1 so that the air space between the protective diaphragm I0 and the operating diaphragm 1 is practically eliminated, which is favorable from an acoustical point of view. This iay be accomplished by the fact that any uctuation oi! pressure is easily compensated for as a result of the expansion of the corrugated portion I6 of the pressure compensation diaphragm Il. In this case the stiffness of the pressure-compensation diaphragm must be small as compared with the stiffness of the protective diaphragm and the operating diaphragm. Any water of condensation formed between the case I and the pressure compensation diaphragm I4 is discharged through openings I9 in the case wall I. The air between the operating diaphragm 1 and the pressure compensating diaphragm I4 acts on the auxiliary diaphragm IB through an opening 20 arranged in the operating diaphragm 1. To easily secure the pressure compensation diaphragm I4 to the protective diaphragm l0, the latter may be provided as will be seen from Fig. 2 with an edge 2| bent at right angles by the deep drawing process which is glued to the edge I1 of the pressure compensating diaphragm I4 also bent at right angles. The electric connection is established on the one hand through the contact piece 2, the elastic cup 3 to the electrode 4 and on the other hand through the wall I through one or more contact foils 22, the bearing ring 9 to the operating diaphragm 1. The walll is insulated from the electrode I and the contact foils are glued to the wall I as indicated at I8 and clamped at one end thereof between the bearing ring 9 and the pressure compensation diaphragm I4. rl'he adhesive substance I8 as will be seen from Fig. 3 may be applied to both sides of the protective diaphragm I0 so that at the point where the contact foil 22 passes a proper sealing may be attained. The wah thickness of the portion I5 of.the pressure compensation diaphragm Il may be so chosen that it may serve as the wall tor the carbon chamber. As will be apparent from Fig. 3 a simple and effective seal is attained which has no detrimental innuence on the acoustical properties of the microphone even in the case oi' fluctuations of temperature. Particular filling bodies and sealing rings are avoided.

What is claimed is:

1. In a microphone, a fixed electrode, a movable electrode, a diaphragm secured to said movable electrode for operating the same,a protective casing for said parts comprising a protective diaphragm in front of said operating diaphragm and a exible pressure compensating diaphragm in the rear thereof, said compensating diaphragm having a peripheral portion which extends past the edge of said operating diaphragm and is sealed to the edge of said protective diaphragm, and an outer casing surrounding said protective casing.

2. In a microphone, a generally cup-shaped casing having a. central opening for a terminal, a corrugated diaphragm having a central cupshaped portion sealed to said casing around said opening, an operating diaphragm in front of said corrugated diaphragm and spaced away therefrom, a protective diaphragm in front of said operating diaphragm and in contact therewith, said corrugated diaphragm having a peripheral portion which is sealed to the edge of said protective diaphragm, means for periph- 5. A microphone as claimed in claim 1, wherein the electrical connection to the movable electrode includes a strip of metal foil which passes through the protective casing at a point where the compensating diaphragm and protective diaphragm are sealed together.

6. A microphone as claimed in claim 2, wherein the central cup-shaped portion ofthe corrugated diaphragm has a greater wail thickness 1 than the remaining portion thereof.

ALBERT UEBERSCH'USS. 

